BLACKLEAD.
This substance, called by mineralogists “plumbago” and “graphite,” is found in small quantities in various districts, and in a very pure state in Cumberland. It is almost pure carbon, having but a very slight admixture of iron; it is used to make blacklead pencils; for coating the surface of iron, giving it a bright appearance and preventing it from rusting; it is also used to prevent friction in wooden machinery, and, mixed with tallow, as a lubricate for iron machinery; blacklead, mixed with clay, is also used to make crucibles for various purposes, these are especially adapted for melting glasses and enamels, and are known in the trade as blue pots.